Organic electroluminescent display device and method of fabricating the same

ABSTRACT

An organic electroluminescent display (OELD) device includes: first and second substrates facing each other; a plurality of gate lines, a plurality of data lines and a plurality of power lines on the first substrate, the gate and data lines crossing each other to define a plurality of pixel regions; a switching element and a driving element connected to each other in each pixel region; a first electrode connected to the driving element; an organic luminescent layer on the first electrode, the organic luminescent layer including a buffer layer as an uppermost layer; and a second electrode of a transparent conductive material on the organic luminescent layer.

The present application claims the benefit of Korean Patent ApplicationNo. 2006-0059348 filed in Korea on Jun. 29, 2006, which is herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic electroluminescent display(OELD) device, and more particularly, to a top emission type OELD devicewith a high luminance and method for fabricating the same.

2. Discussion of the Related Art

In general, organic electroluminescent display (OELD) devices emit lightby injecting electrons from a cathode and holes from an anode into anemission layer, combining the electrons with the holes, generatingexcitons, and transforming the excitons of an excited state to a groundstate. Unlike liquid crystal display (LCD) devices, OELD devices do notrequire an additional light source and therefore have the advantages ofslimness and lightweight.

Since OELD devices have excellent characteristics, such as low powerconsumption, high luminance, fast response time, lightweight and so on,OELD devices can be applied to various electronic products, such asmobile phones, PDAs, camcorders, plam PCs, and so on. Moreover, due totheir simple fabricating process, the fabrication costs of OELD devicesare low as compared with LCD devices.

The OELD devices are divided into a passive matrix type and an activematrix type according to the driving method thereof. The passive matrixtype OELD devices have a simple structure and a simple fabricatingprocess. However, the passive matrix type OELD devices havedisadvantages of high power consumption and low quality images. On theother hand, the active matrix type OELD devices have advantages of highemission efficiency and high quality images.

FIG. 1 is a cross-sectional view illustrating an active matrix type OELDdevice according to the related art.

Referring to FIG. 1, the OELD device 10 includes first and secondsubstrates 12 and 28 facing each other. The first substrate 12 istransparent and flexible. The first substrate 12 has an array element 14including a plurality of thin film transistors (TFTs) T and an organicelectroluminescent diode E including a first electrode 16, an organicluminescent layer 18 and a second electrode 20. The organic luminescentlayer 18 in each pixel region P includes one of red, green and bluecolor materials.

The second substrate 28 includes a moisture absorbent 22 of a powdertype. The moisture absorbent 22 removes moisture inside the OELD device.The moisture absorbent 22 is in a concave portion of the secondsubstrate 28 and is sealed by a taping 25. The first and secondsubstrates 12 and 28 are attached to each other with a seal pattern 26.

In the OELD device, because the first electrode 16 is formed of atransparent material, the light emitted from the organic luminescentlayer 18 travels toward the first substrate 12. Accordingly, it isreferred to as a bottom emission type OELD device.

FIG. 2 is a circuit diagram of an OELD device according to the relatedart.

Referring to FIG. 2, gate and data lines 42 and 44 are formed on asubstrate 32. The gate and data lines 42 and 44 cross each other and aswitching element Ts is formed near the crossing portion of the gate anddata lines 42 and 44. The switching element Ts includes a gate electrode46, a source electrode 56 and a drain electrode 60. The gate electrode46 is connected to the gate line 42. The source electrode 56 separatedfrom the drain electrode 60 is connected to the data line 44.

A driving element Td is electrically connected to the switching elementTs. The driving element Td of a p-type TFT includes a gate electrode 68,a source electrode 66 and a drain electrode 63. The gate electrode 68 ofthe driving element Td is connected to the switching element Ts. Astorage capacitor Cst is formed between the source and gate electrodes66 and 68 of the driving element Td. The drain electrode 63 of thedriving element Td is connected to the first electrode 16 (of FIG. 1) ofthe organic electroluminescent diode E. The source electrode 66 of thedriving element Td is connected to a power line 55.

When a gate signal from the gate line 42 is supplied to the gateelectrode 46 of the switching element Ts, a data signal from the dataline 44 is supplied to the gate electrode 68 of the driving element Tdthrough the switching element Ts. Then, the organic electroluminescentdiode E is driven by the driving element Td such that the organicelectroluminescent diode E emits light. Because the storage capacitorCst maintains a voltage level of the gate electrode 68 of the drivingelement Td, even if the switching element Ts is turned off, the organicelectroluminescent diode E can continuously emit light for apredetermined period of time.

The switching element Ts and the driving element Td include asemiconductor layer of one of amorphous silicon and polycrystallinesilicon. When the semiconductor layer is formed of amorphous silicon,the switching element Ts and the driving element Td can be easilyfabricated.

FIG. 3 is a plan view illustrating an array element of an active matrixtype OELD device according to the related art and FIG. 4 is across-sectional view taken along the line IV-IV of FIG. 3.

Referring to FIGS. 3 and 4, the active matrix type OELD device includesa switching element Ts, a driving element Td and a storage capacitor Cston a substrate 32. Each pixel of the OELD device may include more thanone pair of the switching element Ts and the driving element Td.

A gate line 42 and a data line 44 are formed on the substrate 32 with agate insulating layer interposed therebetween. A pixel region P isdefined by the crossing between the gate and data lines 42 and 44.

The switching element Ts includes a gate electrode 46, an active layer50 and source and drain electrodes 56 and 60. The gate electrode 46 ofthe switching element Ts is connected to the gate line 42, and thesource electrode 56 of the switching element Ts is connected to the dataline 44. The drain electrode 60 of the switching element Ts is connectedto a gate electrode 68 of the driving element Td through a gate contacthole 64.

The driving element Td includes the gate electrode 68, an active layer62 and source and drain electrodes 66 and 63. The source electrode 66 ofthe driving element Td is connected to a power line 55 through a powerline contact hole 58. The drain electrode 63 of the driving element Tdis connected to a first electrode 36 through a drain contact hole 65.The storage capacitor Cst includes the silicon pattern 35 as a firststorage electrode, the power line 55 as a second storage electrode and adielectric layer therebetween.

As illustrated in FIG. 4, an organic electroluminescent diode E includesthe first electrode 36, an organic luminescent layer 38 and a secondelectrode 40. The first electrode 36 contacts the drain electrode 63 ofthe driving element Td through the drain contact hole 65, and theorganic luminescent layer 38 is interposed between the first and secondelectrodes 36 and 40. The first and second electrodes 36 and 40 functionas anode and cathode, respectively.

FIG. 5 is a cross-sectional view illustrating an organicelectroluminescent diode according to the related art.

Referring to FIG. 5, the organic electroluminescent diode E formed on asubstrate 32 includes a first electrode 36, an organic luminescent layer38 and a second electrode 40. Although not shown, the substrate 32includes an array element including the driving element Td (of FIG. 4).The first electrode 36 is connected to the driving element Td (of FIG.4). The first and second electrode 36 and 40 function as anode andcathode, respectively. The organic luminescent layer 38 includes a holeinjection layer (HIL) 38 a, a hole transporting layer (HTL) 38 b, anemitting material layer (EML) 38 c, an electron transporting layer (ETL)38 d and an electron injection layer (EIL) 38 e. The HTL 38 b and theETL 38 d serve to improve emitting efficiency, and the HIL 38 a and EIL38 e serve to reduce energy barrier in injecting electrons and holes.

The second electrode 40 functioning as cathode is formed of a low workfunction material, such as calcium (Ca), aluminum (Al), magnesium (Mg),antigen (Ag) and lithium (Li), and the first electrode 36 functioning asanode is formed of a transparent conductive material such asindium-tin-oxide (ITO).

A sputtering process is generally used to form an ITO layer. However, itis difficult to deposit an ITO layer on the organic luminescent layer 38because of damage on the organic luminescent layer 38 caused by thesputtering process. Accordingly, the OELD device according to therelated art is the bottom emission type in which the first electrode 36of ITO functioning as an anode is formed under the organic luminescentlayer 38. However, the bottom emission type has disadvantages of lowluminance and low aperture ratio. Moreover, because the first electrode36 of ITO functioning as an anode is directly connected to the drivingelement Td, a p-type polycrystalline TFT should be used for the drivingelement Td, thereby complicating the fabrication process of the OELDdevice.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an organicelectroluminescent display (OELD) device and method for fabricating thesame that substantially obviate one or more of the problems due tolimitations and disadvantages of the related art.

An advantage of the present invention is to provide an OELD device witha high luminance.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. These andother advantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described herein, anorganic electroluminescent display (OELD) device includes: first andsecond substrates facing each other; a plurality of gate lines, aplurality of data lines and a plurality of power lines on the firstsubstrate, the gate and data lines crossing each other to define aplurality of pixel regions; a switching element and a driving elementconnected to each other in each pixel region; a first electrodeconnected to the driving element; an organic luminescent layer on thefirst electrode, the organic luminescent layer including a buffer layeras an uppermost layer; and a second electrode of a transparentconductive material on the organic luminescent layer.

In another aspect of the present invention, a method of fabricating anOELD device includes: forming a switching element and a driving elementon a first substrate, the switching and driving elements connected toeach other in a pixel region; forming a first electrode connected to thedriving element; forming an organic luminescent layer on the firstelectrode, the organic luminescent layer including a buffer layer as anuppermost layer; forming a second electrode of a transparent conductivematerial on the buffer layer; and attaching the first substrate to asecond substrate.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a cross-sectional view illustrating an active matrix type OELDdevice according to the related art;

FIG. 2 is a circuit diagram of an OELD device according to the relatedart;

FIG. 3 is a schematic plan view illustrating an array element of anactive matrix type OELD device according to the related art;

FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. 3;

FIG. 5 is a cross-sectional view illustrating an organicelectroluminescent diode according to the related art;

FIG. 6 is a cross-sectional view of an organic electroluminescent diodeaccording to the first embodiment of the present invention;

FIG. 7 is a cross-sectional view of an organic electroluminescent diodeaccording to the second embodiment of the present invention;

FIG. 8 is a schematic plan view illustrating an array substrate for anOELD device according to present invention;

FIGS. 9A to 9D are cross-sectional views taken along the lines IXa-IXa,IXb-IXb, IXc-IXc and IXd-IXd of FIG. 8;

FIGS. 10A to 10E are cross-sectional views illustrating a fabricatingprocess for the portion of the array substrate illustrated in FIG. 9A;

FIGS. 11A to 11E are cross-sectional views illustrating a fabricatingprocess for the portion of the array substrate illustrated in FIG. 9B;

FIGS. 12A to 12E are cross-sectional views illustrating a fabricatingprocess for the portion of the array substrate illustrated in FIG. 9C;and

FIGS. 13A to 13E are cross-sectional views illustrating a fabricatingprocess for the portion of the array substrate illustrated in FIG. 9D.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. The same reference numbers may be used throughout the drawingsto refer to the same or like parts.

FIG. 6 is a cross-sectional view of an organic electroluminescent diodeaccording to the first embodiment of the present invention.

Referring to FIG. 6, the organic electroluminescent diode E is formed ona substrate 100. The organic electroluminescent diode E includes a firstelectrode 132, an organic luminescent layer 142 and a second electrode148. The first electrode 132 and the second electrode 148 function ascathode and anode, respectively. Thus, the second electrode 148 has awork function greater than the first electrode 132. The second electrode148 may be formed of a transparent conductive material such asindium-tin-oxide (ITO), indium-zinc-oxide (IZO), or the like. Theorganic luminescent layer 142 includes EIL 142 a, ETL 142 b, EML 142 c,HTL 142 d and HIL 142 e. A buffer layer 145 is formed between the HIL142 e and the second electrode 148.

When the second electrode 148 is deposited by a sputtering processwithout the buffer layer 145, the HIL 142 e suffers damage. In otherwords, the buffer layer 145 prevents the HIL 142 e from being damagedduring the deposition of the second electrode 148. The buffer layer 145beneficially has a similar property to the HIL 142 e and an impactresistance against deposition of the transparent conductive material.Accordingly, the buffer layer 145 may be formed of one of copperphthalocyanine (CuPC) and vanadium pentoxide (V₂O₅). From an OELD deviceperspective, CuPC has several advantages: a CuPC layer may be formed ina thin film and has a low threshold voltage, a high mobility and a highflexibility.

FIG. 7 is a cross-sectional view of an organic electroluminescent diodeaccording to the second embodiment of the present invention.

Referring to FIG. 7, a buffer-HIL layer 142 f formed of one of the CuPCand the V₂O₅ is formed on the HTL 142 d. The buffer-HIL layer 142 fserves both functions of the HIL 142 e layer (of FIG. 6) and the bufferlayer 145 (of FIG. 6). Unlike the first exemplary embodiment thatrequires two layers, a second electrode 148 can be formed on the organicelectroluminescent diode E without an additional buffer layer.

As described above, the second electrode 148 is formed of a transparentconductive material, such as ITO, IZO, or the like, and the firstelectrode 132 is formed of a metallic material, such as Ca, Al, Mg, Ag,Li, or the like. Because the second electrode 148 formed on the organicelectroluminescent diode E is transparent, the light emitted from theorganic luminescent layer 142 travels upward. Accordingly, the OELDdevice is referred to as a top emission type. The top emission type OELDdevice has a high aperture ratio compared with the bottom emission typeOELD device. Moreover, because the first electrode 132 is formed underthe organic electroluminescent diode E and connected to the drivingelement (not shown) on the substrate 100, an n-type amorphous siliconTFT may be used for the driving element, thereby simplifying thefabrication process and reducing production costs.

FIG. 8 is a schematic plan view illustrating an array substrate for anOELD device according to present invention.

Referring to FIG. 8, the array substrate includes a gate line 106, adata line 126 and a power line 110 formed on a substrate 100. The gateline 106 and the data line 126 cross each other to define a plurality ofpixel regions P on the substrate 100. The power line 110 is parallel toand separated from the gate line 106.

The switching element Ts and the driving element Td, which are connectedto each other, are formed in each pixel region P. The switching anddriving elements Ts and Td include n-type TFTs. The n-type TFT of theswitching element Ts includes a gate electrode 102, an active layer 118a, an ohmic contact layer (not shown) and source and drain electrodes122 a and 122 b. Similarly, the n-type TFT of the driving element Tdincludes a gate electrode 104, an active layer 120 a, an ohmic contactlayer (not shown) and source and drain electrodes 124 a and 124 b. Thedrain electrode 122 b of the switching element Ts is connected to thegate electrode 104 of the driving element Td. The gate electrode 102 ofthe switching element Ts is connected to the gate line 106 such that agate signal is supplied to the gate electrode 102 of the switchingelement Ts though the gate line 106. The source electrode 122 a of theswitching element Ts is connected to the data line 126 such that a datasignal is supplied to the source electrode 122 a of the switchingelement Ts through the data line 126.

A gate pad 108 is formed at an end of the gate line 106, and a gate padelectrode 134 contacts the gate pad 108. Similarly, a data pad 128 isformed at an end of the data line 126, and a data pad electrode 138contacts the data pad 128. A power pad 114 is formed at an end of thepower line 110, and a power pad electrode 136 contacts the power pad114.

A storage capacitor Cst includes a first storage electrode 112, a secondstorage electrode 122 c and a dielectric layer (not shown) therebetween.The first storage electrode 112 extends from the power line 110, and thesecond storage electrode 122 c extends from the drain electrode 122 b ofthe switching element Ts.

The first electrode 132 of the organic electroluminescent diode E (ofFIGS. 6 and 7) is formed on an entire surface of the pixel region P. Thefirst electrode 132 is connected to the drain electrode 124 b of thedriving element Td. Although not shown in FIG. 8, the organicluminescent layer 142 (of FIGS. 6 and 7) and the second electrode 148(of FIGS. 6 and 7) are formed on the first electrode 132. The firstelectrode 132, the organic luminescent layer 142 (of FIGS. 6 and 7) andthe second electrode 148 (of FIGS. 6 and 7) constitute the organicelectroluminescent diode E (of FIGS. 6 and 7).

The switching element Ts and the driving element Td include the n-typeTFTs having the active layers 118 a and 120 a of amorphous silicon,respectively. The source electrodes 122 a and 124 a and the drainelectrodes 122 b and 124 b may have a variety of shapes to improvedriving properties of the switching and driving elements Ts and Td.

For example, as shown in FIG. 8, the source electrode 122 a of theswitching element Ts has a U-shape, and the drain electrode 122 b of theswitching element Ts have a bar shape. A part of the drain electrode 122b is formed inside the U-shape source electrode 122 a and is separatedfrom the U-shape source electrode 122 a. The source and drain electrodes124 a and 124 b of the driving element Td have one of a ring shape and adisc shape. The source electrode 124 a has a disc shape, and the drainelectrode 124 b is in the source electrode 124 a. When the sourceelectrodes 122 a and 124 a and the drain electrodes 122 b and 124 b havethe above-mentioned structures, the channel regions of the n-type TFTs,which are formed between the source electrode 122 a and the drainelectrode 122 b and between the source electrode 124 a and the drainelectrode 124 b, have a lesser length and a greater width than thechannel region of the related art TFT. As a result, the characteristicsof the switching and driving elements Ts and Td are improved.

FIGS. 9A to 9D are cross-sectional views taken along the lines IXa-IXa,IXb-IXb, IXc-IXc and IXd-IXd of FIG. 8.

Referring to FIG. 9A, a switching region S, a driving region D and astorage region C are defined in the pixel region P on the substrate 100.Moreover, a gate region GR, a power region PR and a data region DR areformed at a periphery of the pixel region P. The switching and drivingelements Ts and Td of an n-type TFT are formed in the switching anddriving regions S and C, respectively. The storage capacitor Cst, whichincludes the first and second storage electrodes 112 and 122 c and agate insulating layer 116 therebetween, is formed in the storage regionS. The first and second storage electrodes 112 and 122 c extend from thepower line 110 (of FIG. 8) and the drain electrode 122 b of theswitching element Ts, respectively. The gate insulating layer 116functions as the dielectric layer of the storage capacitor Cst.

The first electrode 132 of an opaque metal material is formed over thedriving element Td in each pixel region P. The first electrode 132contacts the drain electrode 124 b of the driving element Td though athird contact hole CH3. The organic luminescent layer 142 and the secondelectrode 148 are sequentially formed on the first electrode 132. Unlikethe first electrode 132, the second electrode 148 may be formed on anentire surface of the first substrate 100. The first and secondelectrodes 132 and 148 function as anode and cathode, respectively. Thefirst and second electrodes 132 and 148 and the organic luminescentlayer 142 constitute the organic electroluminescent diode E (of FIGS. 6and 7). The organic luminescent layer 142 has a multiple-layer structureas illustrated in FIGS. 6 and 7. A passivation layer 130 is formedbetween the first electrode 132 and the switching element Ts and betweenthe first electrode 132 and the driving element Td.

The switching element Ts in the switching region S includes the gateelectrode 102, the gate insulating layer 116, the active layer 118 a,and the source and drain electrodes 122 a and 122 b. Similarly, thedriving element Td in the driving region D includes the gate electrode104, the gate insulating layer 116, the active layer 120 a and thesource and drain electrodes 124 a and 124 b. The drain electrode 122 bof the switching element Ts is connected to the gate electrode 104through a first contact hole CH1. The drain electrode 124 b is connectedto the power line 110 (of FIG. 8) through a second contact hole and thefirst storage electrode 112.

After forming the first electrode 132, a bank 140 surrounding the pixelregion P is formed such that the organic luminescent layers 142 betweenadjacent pixel regions P do not contact each other.

Referring to FIG. 9B, the gate pad 108 and the gate insulating layer116, the passivation layer 130 and the gate pad electrode 134 are formedin the gate region GR. The gate pad 108 is formed at the end of the gateline 106 (of FIG. 8). The gate pad 108 is formed at the same time as thegate electrodes 102 and 104 (of FIG. 9A). The gate insulating layer 116and the passivation layer 130 have a fourth contact hole CH4. The gatepad electrode 134 contacts the gate pad 108 through the fourth contacthole CH4.

Referring to FIG. 9C, the power pad 114 and the gate insulating layer116, the passivation layer 130 and the power pad electrode 136 areformed in the power region PR. The power pad 114 is formed at the end ofthe power line 110 (of FIG. 8). The power pad 114 is formed at the sametime as the power line 110 (of FIG. 8). The gate insulating layer 116and the passivation layer 130 have a fifth contact hole CH5. The powerpad electrode 114 contacts the power pad 136 through the fifth contacthole CH5.

Referring to FIG. 9D, the data pad 128 and the gate insulating layer116, the passivation layer 130 and the data pad electrode 138 are formedin the data region DR. The data pad 128 is formed at the end of the dataline 126 (of FIG. 8). The data pad 128 is formed at the same time as thedata line 126 (of FIG. 8). The gate insulating layer 116 and thepassivation layer 130 have a sixth contact hole CH6. The data padelectrode 138 contacts the data pad 128 through the sixth contact holeCH6.

FIGS. 10A to 10E are cross-sectional views illustrating a fabricatingprocess for the portion of the array substrate illustrated in FIG. 9A,and FIGS. 11A to 11E are cross-sectional views illustrating fabricatingprocess for the portion of the array substrate illustrated in FIG. 9B.FIGS. 12A to 12E are cross-sectional views illustrating fabricatingprocess for the portion of the array substrate illustrated in FIG. 9C,and FIGS. 13A to 13E are cross-sectional views illustrating fabricatingprocess for the portion of the array substrate illustrated in FIG. 9D.

Referring to FIGS. 10A, 11A, 12A and 13A, the switching, driving andstorage regions S, D and C in the pixel region P and the gate, power anddata regions GR, PR and DR are defined on the substrate 100. The gateelectrodes 102 and 104 in the switching and driving regions S and D, thefirst storage electrode 112 in the storage region S, the gate pad 108 inthe gate region GR and the power pad 114 in the power region PR areformed on the substrate 100 by depositing and patterning a firstconductive metallic material using a patterning mask (not shown). At thesame time, the gate line 106 (of FIG. 8) and the power line 110 (of FIG.8) are formed on the substrate 110. The gate pad 108 is located at theend of the gate line 106 (of FIG. 8), and the power pad 114 is locatedat the end of the power line 110 (of FIG. 8). The first storageelectrode 112 extends from the power line 110 (of FIG. 8). Theconductive metallic material may include at least Al, aluminum alloy(AlNd), chromium (Cr), Molybdenum (Mo), copper (Cu), Titanium (Ti), orthe like.

Next, the gate insulating layer 116 is formed on the substrate 110 bydepositing a first inorganic insulating material. The first inorganicinsulating material may include silicon oxide (SiO₂), silicon nitride(SiNx), or the like.

Next, the semiconductor layer 118 including the active layer 118 a andthe ohmic contact layer 118 b in the switching region S, and thesemiconductor layer 120 including the active layer 120 a and the ohmiccontact layer 120 b in the driving region D are formed on the gateinsulating layer 116 by depositing and patterning an intrinsic amorphoussilicon material and an impurity-doped amorphous silicon material. Thesemiconductor layers 118 and 120 correspond to the gate electrodes 102and 104, respectively.

Next, the first and second contact holes CH1 and CH2 are formed throughthe gate insulating layer 116 by patterning the gate insulating layer116. The first and second contact holes CH1 and CH2 expose the gateelectrode 104 in the driving region D and the first storage electrode112.

Referring to FIGS. 10B, 11B, 12B and 13B, after forming the first andsecond contact holes CH1 and CH2, the source electrodes 122 a and 124 ain the switching and driving regions S and D, the drain electrodes 122 band 124 b in the switching and driving regions S and D, the data pad 128in the data region D and the second storage electrode 122 c in thestorage region C are formed on the substrate 110 by depositing andpatterning a second conductive material. At the same time, the data line126 (of FIG. 8) is formed on the gate insulating layer 116. The secondconductive material includes at least Al, aluminum alloy (AlNd),chromium (Cr), Molybdenum (Mo), copper (Cu), Titanium (Ti), or the like.The source electrode 122 a in the switching region S extends from thedata line 126 (of FIG. 8). The source and drain electrodes 122 a and 122b in the switching region S are separated from each other, and thesource and drain electrodes 124 a and 124 b in the driving region D areseparated from each other. The second storage electrode 122 c extendsfrom the drain electrode 122 b in the switching region S. The drainelectrode 122 b in the switching region S contacts the gate electrode104 in the driving region D through the first contact hole CH1 (of FIG.10A). The drain electrode 124 b in the driving region DR contacts thefirst storage electrode 112 through the second contact hole CH2 (of FIG.10A).

Next, channel regions are defined by removing the ohmic contact layer118 b between the source and drain electrodes 122 a and 122 b in theswitching region S and the ohmic contact layer 120 b between the sourceand drain electrodes 124 a and 124 b in the driving region D. Thechannel regions expose the active layers 118 a and 120 a. In this case,to decrease the length of the channel regions or increase the width ofthe channel regions, the source electrodes 122 a and 124 a may have aU-shape or a ring shape, and the drain electrodes 122 b and 124 b mayhave a bar shape or a disc shape. The drain electrodes 122 b and 124 bare separated from the source electrodes 122 a and 122 b.

Referring to FIGS. 10C, 11C, 12C and 13C, the passivation layer 130 isthen formed on the substrate 110 by depositing a second inorganicinsulating material. The second inorganic insulating material includesat least silicon oxide (SiO₂), silicon nitride (SiNx), or the like.Next, the third to sixth contact holes CH3, CH4, CH5 and CH6 are formedthrough the passivation layer 130 by patterning the passivation layer130. The third and fourth contact holes CH3 and CH4 expose the drainelectrode 124 b in the driving region D and the gate pad 108 in the gateregion GR, respectively, and the fifth and sixth contact holes CH5 andCH5 expose the power pad 114 in the power region PR and the data pad 128in the data region DR, respectively.

Referring to FIGS. 10D, 11D, 12D and 13D, the first electrode 132, thegate pad electrode 134, the power pad electrode 136 and the data padelectrode 138 are then formed on the passivation layer 130 by depositingand patterning a metallic material, such as Ca, Al, Mg, Ag, Li, or thelike. The first electrode 132 and the gate pad electrode 134 contact thedrain electrode 124 b in the driving region D and the gate pad 108through the third and fourth contact holes CH3 and CH4, respectively.The power pad electrode 136 and the data pad electrode 138 contact thepower pad 114 and the data pad 128 through the fifth and sixth contactholes CH5 and CH6, respectively.

Next, the bank 140 is formed on the substrate 100 to surround the pixelregions P by depositing and patterning a third organic insulatingmaterial. The third organic insulating material includes at leastbenzocyclobutene (BCB), acrylate resin, or the like. Because the bank140 surrounds the pixel region P, the first electrode 132 in the pixelregion P, the gate pad electrode 134, the power pad electrode 136 andthe data pad electrode 138 are exposed by the bank 140. The bank 140prevent the organic luminescent layers 142 (of FIG. 9A) in adjacentpixel regions P from contacting each other.

Referring to FIGS. 10E, 11E, 12E and 13E, the organic luminescent layer142 is then formed on the first electrode 132. The organic luminescentlayer 142 has the EIL 142 a, the ETL 142 b, the EML 142 c, the HTL 142d, the HIL 142 e and the buffer layer 145. Alternatively, as illustratedin FIG. 7, the organic luminescent layer 142 may have the EIL 142 a, theETL 142 b, the EML 142 c, the HTL 142 d, and the buffer-HIL 142 f (ofFIG. 7).

Next, the second electrode 148 is formed on the organic luminescentlayer 142 by depositing and patterning a transparent conductivematerial. The transparent conductive material includes ITO, IZO, or thelike. The first and second electrodes 132 and 148, and the organicluminescent layer 142 therebetween constitute the organicelectroluminescent diode E.

The lower substrate of the OELD device having the array element and theorganic electroluminescent diode is fabricated by the processesdescribed above. A top emission type OELD device according to thepresent invention is completed by attaching the lower substrate and aupper substrate including a moisture absorbent using a seal pattern.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. An organic electroluminescent display (OELD) device, comprising:first and second substrates facing each other; a plurality of gatelines, a plurality of data lines and a plurality of power lines on thefirst substrate, the gate and data lines crossing each other to define aplurality of pixel regions; a switching element and a driving elementconnected to each other in each pixel region; a first electrodeconnected to the driving element; an organic luminescent layer on thefirst electrode, the organic luminescent layer including a buffer layeras an uppermost layer; and a second electrode of a transparentconductive material on the organic luminescent layer.
 2. The deviceaccording to claim 1, wherein the buffer layer includes one of CuPC andV₂O₅.
 3. The device according to claim 2, wherein the organicluminescent layer further includes an electron injection layer on thefirst electrode, an electron transporting layer on the electroninjection layer, an emitting material layer on the electron transportinglayer and a hole transporting layer on the emitting material layer. 4.The device according to claim 1, wherein the organic luminescent layerincludes an electron injection layer on the first electrode, an electrontransporting layer on the electron injection layer, an emitting materiallayer on the electron transporting layer, a hole transporting layer onthe emitting material layer and a hole injection layer on the holetransporting layer.
 5. The device according to claim 1, furthercomprising a storage capacitor including first and second storageelectrodes and a dielectric layer between the first and second storageelectrodes, wherein the first and second storage electrodes extend fromthe power line and the switching element, respectively.
 6. The deviceaccording to claim 1, wherein each of the switching and driving elementsincludes a gate electrode, a semiconductor layer and source and drainelectrodes separated from each other, and wherein the drain electrode ofthe switching element is connected to the gate electrode of the drivingelement, and the first electrode is connected to the drain electrode ofthe driving element.
 7. The device according to claim 6, wherein thesource electrode of one of the switching and driving elements includesone of a U-shape and a ring shape, and the drain electrode of one of theswitching and driving elements includes one of a bar shape and a discshape.
 8. The device according to claim 6, further comprising: a gatepad at an end of the gate line; a data pad at an end of the data line;and a power pad at an end of the power line.
 9. The device according toclaim 8, wherein the gate line, the gate pad, the power line and thepower pad are formed of a same layer and with a same material as oneanother.
 10. The device according to claim 6, wherein the semiconductorlayer includes amorphous silicon.
 11. The device according to claim 1,wherein the transparent conductive material includes one of ITO and IZO.12. The device according to claim 1, wherein a work function of thefirst electrode is lower than a work function of the second electrode.13. The device according to claim 12, wherein the conductive materialincludes one of Ca, Al, Mg, Ag and Li.
 14. The device according to claim1, wherein the first electrode is formed in each pixel region, and thesecond electrode is formed on an entire surface of the first substrate.15. The device according to claim 1, wherein the buffer layer functionsas a hole injection layer.
 16. A method of fabricating an OELD device,comprising: forming a switching element and a driving element on a firstsubstrate, the switching and driving elements connected to each other ina pixel region; forming a first electrode connected to the drivingelement; forming an organic luminescent layer on the first electrode,the organic luminescent layer including a buffer layer as an uppermostlayer; forming a second electrode of a transparent conductive materialon the buffer layer; and attaching the first substrate to a secondsubstrate.
 17. The method according to claim 16, wherein the bufferlayer includes at least one of CuPC and V₂O₅.
 18. The method accordingto claim 16, wherein forming the organic luminescent layer furthercomprises: forming an electron injection layer on the first electrode;forming an electron transporting layer on the electron injection layer;forming an emitting material layer on the electron transporting layer;and forming a hole transporting layer on the emitting material layer.19. The method according to claim 18, wherein forming the organicluminescent layer further comprises forming a hole injection layerbetween the hole transporting layer and the buffer layer.
 20. The deviceaccording to claim 18, wherein the buffer layer functions as a holeinjection layer.